1. Field of the Invention
The present invention is directed to a polymeric composition useful as an electric conduit covering More particularly, the present invention is directed to a polymeric composition of a high density ethylene polymer, a high melt index ethylene polymer and an organic peroxide which is particularly useful as an electrical conducting covering.
2. Background of the Prior Art
The manufacture of insulated electrical conduits comprising an electrical conductor, i.e., wires and cable, covered by an insulating material is a major industrial product used throughout the world. Because of the importance of this manufactured commodity, all aspects of this product have continually been the subject of new developments. A particularly important area of this development has focused on the insulating covering of the electrical conduit.
Although all aspects of the electrical conduit covering art are subject to the new developments mentioned above, certain aspects of electrical conduit coverings still require further development to overcome the problems long appreciated by those skilled in the art. Two such areas involve processability of the polymeric composition used as the conduit covering and the shrinkback characteristics of the conduit covering itself.
The production of an electrical conduit involves coating a moving wire with a polymeric composition. This process usually involves extruding the polymeric composition as a melt onto the moving electrical conductor to be coated The difficulties associated with extruding the polymeric melt onto the electrical conductor are recognized in the art. Thus, the ease with which the polymeric composition can be extruded, that is, the processability of the polymeric composition, is an important indecia of the effectiveness of the coating process. Thus, the art recognizes the desirability and importance of improving the polymeric composition processability characteristic in electrical conduit manufacture.
The second, above-mentioned problem associated with covered electrical conduits, the so-called "shrinkback" phenomenon, originates in the electrical conduit forming operation. In order to produce electrical insulated conduits in an efficient matter the rate of covering of electrical wires, cables and the like must be rapid. This rate of covering produces stress in the polymeric composition coating which is manifested by stress release when the insulated electrical conduit is cut Upon slitting the electrical conduit, for use in various applications, the covering tends to "shrinkback." This results in uncoated electrical wire at the point of cutting. Those skilled in the art are aware of the safety hazards, inefficiencies and the like manifested by uncovered electrical conductors. Indeed, this problem is so well recognized in the art that electrical conduit manufacturers impose shrinkback standards. The length allowed for shrinkback of insulating coverings from slit electrical conduit is the subject of electrical conduit manufacturers' standards. Polymeric composition manufacturers producing products for this market oftentimes find it difficult formulating compositions which meet this shrinkback requirement without compromising other characteristics required of a polymeric cable covering.
In summary, the electrical conduit covering art, although producing a great variety of polymeric compositions which meet the needs of cable manufacturers, recognizes a continuing need to produce improved polymeric compositions, useful as electrical conduit coverings, which possess improved processability characteristics during electrical conductor covering operations and exhibit decreased shrinkback when utilized as a covering for electrical conduits.